2.3
Mediterranean Lee Cyclogenesis
Ron McTaggart-Cowan, MSC, Montreal, QC, Canada; and T. J. Galarneau and L. F. Bosart
This study investigates the formation and intensification of a
rapidly-developing cyclone that formed in the Gulf of Genoa on 15
November 2007. This region has been shown to be
climatologically active in terms of lee cyclogenesis; however studies
investigating Gulf of Genoa development
focus almost entirely on the role of the Alps in the dynamics of the
cyclgenetic process.
The symmetric, spiral nature of the mature system, combined with
satellite observations that suggest the presence of a deep warm core
at its centre, leads to the hypothesis that the November 15 cyclone
(whose near-surface winds reached 50 kt) extracted and converted
significant energy from the warm underlying Mediterranean waters in
the form of latent heat fluxes and deep moist convection. These
processes have been shown to be fundamentally important for the
formation of both
Mediterranean hurricanes and polar lows, both of which are
structurally similar to the "lee cyclone" studied here.
In order to identify the cyclogenetic mechanisms fundamental to this
case, a modelling study has been undertaken using the Canadian
Meteorological Centre's Mesoscale Alpine Project (MAP D-PHASE) domain,
run operationally over this period in support of the D-PHASE
operational period. Using time-varying orography to reduce shock wave
generation, a series of tests involving the removal of flow-modifying
terrain (the Alps, the Massif Centrale, the Pyrenees, the Appenines,
and the islands of Sardinia and Corsica) are preformed. The intensity
and location of the resulting cyclone is not dramatically affected by
these extreme changes to the local orography, but the structure of the
system appears to depend on the presence of the mountain ranges.
Combining the current theories of lee cyclogenesis, polar lows and
mediterranean hurricanes, this study demonstrates that the November 15
case of lee cyclogenesis is significantly influenced by the presence
of warm Mediterranean waters beneath the cold northerly flow behind
the trough. The resulting hybrid storm is baroclinically
driven, but its intensity enhanced by the developed of reduced
convective
stability over the Gulf of Genoa.
Recorded presentationSession 2, Weather Forecasting II
Monday, 11 August 2008, 10:30 AM-12:00 PM, Rainbow Theatre
Previous paper Next paper